Diagnosis and therapy are two main categories in clinical application of diseases, and recently, a concept of theragnosis which is a technology simultaneously performing diagnosis and therapy utilizing an imaging function in an anti-cancer drug has been introduced. For a successful theragnosis, an imaging agent and a drug are required to be effectively delivered to a target disease area. There are many cases that drug is not delivered as enough to show efficiency of a drug in a target disease area in a drug delivery process, such that an actual effect is not obtained in a clinical therapy, wherein in a serious case, the drug is administered in a body and delivered to a normal tissue rather than the corresponding tissue, thereby causing severe side effect.
In addition, since the diagnosis of the corresponding disease is possible only when an imaging agent is delivered to a target specific area, a method of effectively delivering the drug and the imaging agent to a target area is required (Acc. Chem. Res., 2011, 44 (10), pp 1018-1028).
As the imaging modality, fluorescence optical imaging, magnetic resonance imaging (MRI), positron-emission tomography (PET) and computed tomography (CT), and the like, have been utilized. The imaging agent used in the imaging modality equipment has been variously developed. In particular, in view of diagnosis and therapy of the disease, a magnetic nanoparticle has advantages of being non-toxic, having excellent biocompatibility, being injected through blood vessel, and being accumulated in a high content in human tissue (Taeeok Kim, nano-biotechnology, Biotech Policy Research Center, 2009).
The magnetic nanoparticles in a nano-bio field have been used in wide range of applications such as separation of biological materials, magnetic resonance imaging diagnosis imaging agent, a biosensor including a giant magneto resistive sensor, drug/gene delivery, magnetic therapy at high-temperature, and the like. Specifically, the magnetic nanoparticle may be used as an imaging agent for diagnosing a molecular magnetic resonance imaging. The magnetic nanoparticles shorten a spin-spin relaxation time of the hydrogen atoms of water molecules around the nanoparticles to amplify MRI signal, which is widely and currently used in resonance imaging diagnosis.
In addition, the magnetic nanoparticle may also be used in therapy in vivo through delivery of drug or gene. The drug or the gene is loaded on the magnetic nanoparticle by chemical bond or absorption and moved to a desired position by an external magnetic field, and the drug and the gene are discharged to a specific area to bring selective therapy effect (see Korean Patent Publication No 0819378). Currently, as a mean of delivering the drug using the magnetic nanoparticle, magnetic liposome has emerged as the most powerful tool. The magnetic liposome has a form in which magnetic nanoparticles are contained in liposome surrounded with phospholipid layers and contains the drug, the gene, and the like, in the liposome, to be delivered to a specific area (Toshihiro Matsuo et al., J. Biomedical Materials Research Part A, 66A(4): 747-754, 2003). In addition, the magnetic nanoparticles may have a function of tracking a specific tissue by chemical therapy of the surface of liposome. Recently, a magnetic cationic liposome (MCL) increasing adsorption and accumulation properties in a biotissue was developed in order that the magnetic liposome effectively tracks cancer cell (XiaoliZheng et al., International J. Pharmaceutics, 366:211-217, 2009). However, a stable magnetic nanoparticles having improved biocompatibility and stability is still required.
In addition, when the nanoparticles are injected in vivo, long circulating property in which the nanoparticles are well-dispersed and circulated for an appropriate time without agglomeration in blood is required. However, since the nanoparticle has a large surface area, the nanoparticles are well-agglomerated due to a biofouling phenomenon that various plasma protein, salts, and the like, are well attached to the nanoparticles, to thereby be easily removed by reticuloendothelial cells (reticuloendothelial system: RES) such as Kuffer cell of liver, macrophage of spleen. Therefore, within several minutes after injecting the nanoparticles into the body, the nanoparticles disappear in blood and may not reach to the desired tissue. In addition, when iron oxide nanoparticles are not sufficiently stabilized in vivo, the original structure thereof is changed, such that magnetic property may be changed or biodegradation may rapidly occur. Therefore, a technology of coating a surface of a nanoparticle using polymer such as polyethylene glycol (PEG) to increase biocompatibility and stability has been studied (Polymer Science and Technology. Vol 19 (2). 2008. 116-124).
Meanwhile, it was found that siRNA has remarkable effect in inhibiting expression of a specific gene in an animal cell, and thus, is being focused as a gene therapeutic agent, and due to high activity and precise gene selectivity thereof, siRNA is expected to be an alternative therapeutic agent to antisense oligonucleotide (ODN) currently being used as a therapeutic agent as a result of the past 20-year's research (Dana J. Gary et al. Journal of Controlled Release 121:64-73, 2007).
In particular, siRNA techniques used with the therapeutic purpose has a large advantage of being easily designed as compared to other medical products and effectively inhibiting expression of a specific gene, and high target selectivity and the gene expression inhibition by RNAi of siRNA, and the like, uses mechanism naturally present in vivo to have low toxicity. In addition, the nanoparticle in which a material capable of binding to receptor present in a specific area is bound with drug capable of killing cancer cell, and the like, may deliver the drug with the specific cell as a target.
The biggest challenge which is required to be overcome in treating diseases such as cancer, and the like, is to develop a technology of selecting an appropriate ‘target material (targeting agent)’ capable of precisely and selectively delivering the nanoparticles containing therapeutic agent to a target tissue of cancer cell, and the like, and binding the target material to the nanoparticles. The target material or ligand bound to the nanoparticles needs to be bound to a surface of tumor cell by an appropriate method to operate the receptor, thereby enabling endocytosis the anticancer agent contained in the nanoparticles in cells (Junung, Lee, nanoparticles and target tracking system for cancer therapy, a high-tech information analysis report, Korea Institute of Science and Technology Information, 2004).
Recently, in order to improve an intracellular delivery efficiency of siRNA, technology of using a siRNA conjugate in which hydrophilic material which is a biocompatible polymer (for example, polyethylene glycol (PEG) is bound to the siRNA by a simple covalent bond or a linker-mediated covalent bond, to thereby secure stability of siRNA and have effective cell membrane penetrability was developed (see Korean Patent Publication No. 883471). However, the conjugation (PEGylation) of the polyethylene glycol (PEG) to the siRNA still has disadvantages in that stability is low in vivo and delivery to the target tissue is not smooth.
In order to solve the problem, a double-stranded oligo RNA structure in which the hydrophilic material and the hydrophobic material are bound to the double-stranded oligo RNA was developed, the double-stranded oligo RNA structure forms self-assembling nanoparticles by a hydrophobic interaction of the hydrophobic material. The self-assembling nanoparticle is referred to as ‘SAMiRNA’ (Korean Patent Laid-Open Publication No. 2009-0042297).